This invention relates to an actuating drive of an air passage device for an engine cooling system of a vehicle.
Such actuating drive comprises a drive gear to be driven by an electric motor, which is rotatable about an axis of rotation, and an output element which is operatively connected with the drive gear and is movable with the drive gear along an adjustment path, in order to shift the air passage device between an open position, in which the air passage device is opened in order to allow an air stream to pass through, and a closed position in which the air passage device is closed in order to minimize the air stream.
Such air passage device can be arranged for example at the front of the vehicle and control an air stream into an engine compartment of the vehicle. For this purpose, the air passage device for example can include closing elements in the manner of slats, which can be shifted in order to vary the flow cross-section for the air stream and in this way adjust an air stream for cooling an engine in the engine compartment.
Such air passage devices are well-known in different designs. By way of example, reference is made to DE 10 2008 013 422 A1 and DE 100 47 952 B4.
Conventional actuating drives of passage devices often use a so-called vacuum cell with a spring-biased membrane. With such a vacuum cell, a membrane is moved by a solenoid valve against a biasing spring and a vacuum is passed on, which effects an adjustment force for shifting the air passage device in direction of its closed position.
Such vacuum cells have the advantage that they have a simple construction and are available at low cost. In addition, they have an inherent safety function in that in the case of a failure of the energy supply system of the vehicle an opening of the air passage device is effected automatically, because the electromagnetic force on the membrane decreases and due to the spring action the membrane moves the air passage device back into its open position (so-called “fail-safe” logic). In the case of a failure of the electrical supply of the actuating drive, and in case a further electromotive control of the air passage device is not possible, the air passage device thus is automatically moved into its open position, so that an air cooling of an engine to be cooled still is ensured.
It is desirable, however, to use an electromotive driving device, for example an electric step motor, for an actuating drive instead of such vacuum cell. A disadvantage when using a vacuum cell consists in that it must be formed comparatively large, in order to be able to apply a sufficient adjustment force for closing an air passage device. This is due to the fact that in an air passage device slats possibly must be moved against a pressing wind force at a great driving speed of a vehicle, so that large adjustment forces are required for moving the slats. The use of an electromotive driving device on the other hand has the advantage that the same can be dimensioned comparatively small. The required adjustment force then is achieved in that the electromotive driving device is coupled with an output element via a reduction gear for shifting the air passage device, so as to transmit a drive movement of the driving device in a stepped-down manner into an output movement of the output element.
When a reduction gear is used, the same can effect self-locking or a high reaction torque in the drive train of the actuating drive. This is not disadvantageous as such, but leads to the fact that in the case of a failure of the energy supply system resetting of the air passage device into its open position for increasing the flow cross-section is not easily possible, because the self-locking actuating drive blocks adjustment forces acting on the output side, and shifting of the air passage device thus only is possible via the actuating drive.
From DE 10 2009 035 362 A1 an actuating drive for an air passage device is known, which provides two separate actuating devices, namely on the one hand a normal-operation actuating device and on the other hand an emergency-operation actuating device. The operation of the actuating devices is controlled thermally: when a temperature of a predetermined region of the vehicle is below a threshold temperature, only the normal-operation actuating device is active and coupled with an output element; when the temperature however is above the threshold temperature, the normal-operation actuating device is decoupled from the output element, and the emergency-operation actuating device moves the output element in direction of an opening of the air passage device.